In modern piping systems, the use of pipes made from plastics or the like, is becoming increasingly common. These materials have a tendency to cold flow, i.e. to undergo slow change in shape when they are subjected to mechanical pressure over a period of time. This causes problems concerning connection of the pipes to nipples, pipe stubs and the like, since clips known up to now were designed for pipes of elastic material such as rubber. It is thus necessary to retighten the clips at periodic intervals, if such clips are used on pipes having a cold flow tendency.